A flexible tank on board a vehicle may contain kerosene for feeding to a rotorcraft gas turbine engine, for example, or may contain water for fire-fighting if the vehicle is a water-bombing helicopter, in particular.
When the vehicle moves, the liquid itself moves inside the tank leading to the liquid level rising on one side of the tank and falling on the other side of the tank, resulting in sloshing that can lead to numerous inconveniences. Such sloshing can lead to hammering that might damage the structure of the vehicle, or to a shift in its center of gravity, which is harmful to the balance of the vehicle and makes it difficult to pilot, particularly if it is a helicopter type rotorcraft.
Document U.S. Pat. No. 6,622,966 discloses a first device having a ballasted float placed on the liquid contained in the tank. The purpose of the float is to keep the liquid level so that its surface remains parallel to the bottom of the tank. In that way, the sloshing phenomenon is prevented from occurring.
Nevertheless, it is possible that a sudden movement of the vehicle can overcome the force exerted by the float, thereby reducing its effectiveness.
Document WO 2005/014394 discloses a second device having a plate inserted inside a tank. The plate also co-operates with two wormscrews controlled by a motor so as to enable the plate to move vertically. Thereafter, the motor drives the wormscrews to move the plate so that it is held against the surface of the liquid in such a manner as to keep said surface horizontal, in the frame of reference of the vehicle, naturally.
Nevertheless, in order to operate, that second device needs electrical power to be delivered thereto from outside the device. Unfortunately, power is a particularly precious resource on board a vehicle, in particular an aircraft, and that can impede implementing the second device.
Furthermore, the motor needs to be controlled properly to ensure that the plate remains continuously in a suitable position, both while the vehicle is being used and while the tank is being filled. This control needs to be extremely accurate and involves complex control relationships and/or control and monitoring means that are onerous, both from a financial point of view and from the point of view of the weight of the device.
Finally, document FR 2 829 103 discloses a third device in which the top portion of a tank is put under pressure by an actuator or by tensioners.
The use of tensioners presents the disadvantage of not enabling the pressure exerted on the surface of the liquid to be adjusted while the vehicle is in use. Consequently, if the level of the liquid is modified during said use, the action of the tensioners runs the risk of being found to be insufficient.
Furthermore, the use of actuators presents the above-mentioned potential drawbacks, and in particular those associated with making such a device difficult to control.